The first example of green (λ > 500 nm)-to-ultraviolet (λ < 400 nm) triplet–triplet annihilation-based photon upconversion sensitized by lead halide perovskite nanocrystals is achieved.
Visible‐to‐ultraviolet (vis‐to‐UV) triplet‐triplet annihilation based photon upconversion (TTA‐UC) is achieved in a non‐volatile chromophoric ionic liquid (IL) for the first time. A novel IL is synthesized by combining UV‐emitting anion 4‐(2‐phenyloxazol‐5‐yl)benzenesulfonate (PPOS) and trihexyltetradecylphosphonium cation (P66614). The nanostructured organization of chromophoric anions is demonstrated by synchrotron X‐ray and optical measurements. When the IL is doped with a triplet sensitizer tris(2‐phenylpyridinato)iridium(III) (Ir(ppy)3), the visible‐to‐UV TTA‐UC with a relatively low threshold excitation intensity of 61 mW cm−2 is achieved. This is due to a large triplet diffusion coefficient in the IL (1.4×10−7 cm2 s−1) as well as a high absorption coefficient 15 cm−1 and a long PPOS triplet lifetime of 1.55 ms, all implemented in the condensed IL system. This work demonstrates the unique potential of ILs to control chromophore arrangements for desired functions.
Invited for this month's cover picture is the group of Professor Nobuhiro Yanai and Nobuo Kimizuka at Kyushu University. The cover picture shows visible‐to‐ultraviolet (vis‐to‐UV) triplet‐triplet annihilation‐based photon upconversion (TTA‐UC) via triplet exciton diffusion in a chromophoric ionic liquid (IL). Chromophore moieties spontaneously form continuous arrays in non‐polar nano‐domains of the IL. The close arrangement of the chromophores in the IL allowed effective diffusion of triplet excitons, resulting in the vis‐to‐UV TTA‐UC at a low excitation intensity. Read the full text of their Communication at 10.1002/open.201900304.
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